This invention relates to instrument guidance for stereotactic surgery.
Stereotactic localization is a method for locating a target within a three-dimensional object. This method is used in the medical arts and sciences to locate a target in the human body, in particular in the brain or spine, for medical and surgical treatment. Stereotactic surgery has a history dating back to the turn of the century, when the Horsely-Clark Apparatus was described as a mechanical frame system in which an animal was immobilized. This frame system permitted reproducible targeting within the animal""s brain for physiological experiments. This and similar technology found application in 1948 in the work of Wycis and Speigel. In their work, a frame was attached to a human skull. The frame permitted targeting of sites within the human brain for neurosurgical treatment. A detailed survey of the field of stereotactic surgery can be found in Textbook of Stereotactic and Functional Neurosurgery, P. L. Gildenberg and R. R. Tasker (eds.), McGraw-Hill, June 1997 (ISBN: 0070236046).
One approach to stereotactic surgery involves the following steps. Fiducial scanning markers are attached to the body in one of a variety of manners, including using an attachable frame or attaching the markers to the skin with an adhesive. A scan is then taken of a body, for example of the head, to produce a three-dimensional image of the body. Scanning can be done using a variety of techniques including CT, MRI, PET, and SPECT. Images of the fiducial scanning markers that are located around the body are then located in the three-dimensional image at fiducial image points. Points of interest, such as the location of a tumor, are located in the three-dimensional image with reference to these fiducial image points. The body and the image are registered by matching the locations of the scanning markers and the coordinates of the fiducial image points. In an approach to stereotactic brain surgery, a three-dimensional frame is screwed to the patient""s skull prior to scanning the head. This frame serves as a mechanical reference mechanism that supports scanning fiducial markers at fiducial points around the body. The frame remains attached to the patient""s skull from before scanning until after surgery is complete. Prior to surgery, a mechanical guide assembly is attached to the frame. The relative location in the image of the point of interest with respect to the fiducial image points is determined, and this relationship is used to adjust the mechanical guide assembly with respect to the fiducial points on the frame. Using the adjusted mechanical guide assembly, a surgical instrument is then guided to a location in the body that corresponds to the point of interest in the image.
In another form of stereotactic surgery, known generally as xe2x80x9cimage-guidedxe2x80x9d stereotactic surgery, rather than relying on mechanical adjustment of a guide assembly, visual feedback is provided to a surgeon by displaying a composite image formed from the scanned three-dimensional image and a synthesized image of a hand-held surgical instrument. The surgeon guides the hand-held instrument into the body using the visual feedback. In this form of surgery, a frame is attached to the patient and a scan is taken as described above. After scanning, the head and frame are secured in a fixed position, for example, fixed to an operating table. In order to display the image of the surgical instrument in a proper relationship to the scanned image, the position and orientation of the instrument is sensed using a localization apparatus that remains in a fixed position relative to the body. The localization apparatus can be coupled to the surgical instrument using an articulated mechanical arm on which the surgical instrument is attached. Sensors in the joints of the arm provide signals that are used to determine the location and orientation of the instrument relative to a fixed base of the mechanical arm. Some more recent systems do not use mechanical coupling between the surgical instrument and the localization apparatus and instead rely on remote sensing of small localized energy emitters (e.g., sources or transducers of energy) fixed to the instrument. For example, a camera array is used to locate light-emitting diodes (LEDs) that are attached to the instrument. The locations of the LED images in the camera images are used to determine the three-dimensional physical locations of the LEDs relative to the camera array. The locations of multiple LEDs attached to the instrument are then used to determine the location and orientation of the instrument. Another example of remote sensing uses sound generators and a microphone array and relies on the relative time of arrival of acoustical signals to determine the three-dimensional locations of the sound generators.
Before a synthesized image of the instrument can be combined with the scanned image in a proper relationship, some form of registration is required. For example, the tip of the surgical instrument can be placed at each of several fiducial markers for which corresponding images have been located in the three-dimensional scanned image. Registration of the synthesized image of the instrument and the scanned image can thereby be established.
In a variant of image-guided stereotactic surgery, generally known as xe2x80x9cdynamic referencing, xe2x80x9d the head and frame are secured in a fixed position, as in the image-guided approach. However, unlike other image-guided techniques, the sensors (e.g., cameras) of the localization apparatus are not at a fixed location. In order to compensate for the motion of the sensors, energy emitters are fixed to the frame as well as to the instrument. At any point in time, the location and orientation of the frame relative to the sensors as well as the location and orientation of the instrument relative to the sensors are both determined, and the differences in their locations and orientations are used to compute the location and orientation of the instrument relative to the frame. This computed location of the instrument is then used to display the synthesized image of the surgical instrument in an appropriate relationship to the scanned image.
Still another approach to stereotactic surgery, generally known as xe2x80x9cframeless image-guidedxe2x80x9d stereotactic surgery, does not rely on attaching a frame to the body before scanning. Instead, adhesive fiducial scanning markers are applied to the scalp, or small screws are inserted into the skull, and the patient is scanned as in the techniques described above. During surgery, the patient is immobilized and locked in place using a head clamp or a frame. The image-guided stereotactic approach described above is then followed, including the registration procedure described above to establish the locations of the fiducial scanning markers relative to the instrument.
In image-guided techniques, a surgeon can rely on a variety of views of a three dimensional scanned image. These views can include a three-dimensional surface view with an adjustable point of view (e.g., a perspective view with surface shading). In addition, planar (i.e., two-dimensional) views of the image can be displayed. In particular, three two-dimension xe2x80x9cslicesxe2x80x9d through orthogonal planes of the image are typically displayed, with the orientations of the planes being sagittal (dividing a head into a left and a right part), coronal (dividing a head into a front and a back part), and axial (dividing a head into an upper and lower part). As the orientations of the planes are predetermined, the particular planes that are displayed can be determined by the point of intersection of the three planes. A point, such as the tip of a probe, can be displayed in a three-dimensional surface view as a point in a appropriate geometric relationship. The point can be displayed in a planer view by orthogonally projecting the point onto the associated plane. A line can be displayed in a planar view as an orthogonal projection onto the associated plane, or as the point of intersection of the line and the associated plane. Note that if a first point, such as a surgical entry point is used to determine which planes are displayed, a second point, such as a surgical target point, does not in general fall in any of the displayed planes.
Planar views of a three-dimensional scan can also use alternative orientations than the standard sagittal, coronal, and axial orientations described above, allowing two points to lie in two orthogonal planes, and one of the two points to additionally lie in a third orthogonal plane. In particular, a xe2x80x9cnavigationalxe2x80x9d view can be determined according to two points in an image, such as an entry point at the surface of a body and a target point within the body. The line joining the entry point and the target point is chosen as the intersection of two orthogonal planes, navigation planes 1 and 2. The orientation of navigational planes 1 and 2 is arbitrary (that is, the two planes can be rotated together around their intersecting line). A third plane, orthogonal to navigation planes 1 and 2, provides a xe2x80x9cbird""s eyexe2x80x9d view looking from the entry point to the target point. This bird""s eye plane is typically chosen to pass through the target point. (Such a navigational view is shown in FIG. 14a). Using a navigational view, the orientation of a surgical instrument is typically shown as a line projected orthogonally onto the two navigational planes, and as the point of intersection of the line and the bird""s eye plane. Manipulating an instrument using such a navigational view for feedback requires considerable practice and is not intuitive for many people.
Image-guided frameless stereotaxy has also been applied to spine surgery. A reference frame is attached to an exposed spinous process during open spine surgery, and a probe is used to register the patient""s spine with scanned image of the spine. Anatomical landmarks are used as fiducial points which are located in the scanned image. Visual feedback is provided to manually guide placement of instruments, such as insertion of pedicle screws into the spinal structures.
In one aspect, in general, the invention is a method for stereotactic surgery on a body, such as surgery on the brain or spine. The method includes first providing a guidance fixture that includes (a) a mounting base having a central axis, (b) a controllable instrument drive for moving a surgical instrument along a constrained trajectory in response to a drive control signal, (c) an actuated adjustment mechanism coupled between the mounting base and the controllable instrument drive, and (d) a sensor system coupled to the adjustment mechanism. The mounting base of the guidance fixture is attached to the body and a location of the mounting base in a three-dimensional image of the body is determined, for example, using a remote sensing device, such as a camera, and tracking markers, such as LEDs, attached to the guidance fixture. Sensor signals encoding the orientation of the constrained trajectory and encoding a position of the surgical instrument along the constrained trajectory are generated and transmitted from the guidance fixture.
The method can include one or more of the following features:
An adjustment control signal is received and the orientation of the constrained trajectory relative to the mounting base is adjusted in response to the received adjustment control signal.
The orientation of the constrained trajectory is adjusted by rotating the instrument drive about the central axis and adjusting an angle between the instrument drive and the central axis.
The sensor signals are received and a location of the surgical instrument is determined in the three-dimensional image using the sensor signals and the determined location of the mounting base in the three-dimensional image.
A control input is accepted from an operator, the adjustment control signal is determined from the control input, and then the adjustment control signal is transmitted.
A force feedback signal is generated in response to adjustment of the guidance fixture and the force feedback signal is transmitted to the operator.
A view of the three-dimensional image is displayed in conjunction with a representation of the location of the surgical instrument.
The adjustment control signal is determined by executing of an automated procedure, for example, by executing a stored program on a computer for determining the adjustment control signal from the accepted control signal and the determined location of the surgical instrument.
In another aspect, in general, the invention is an apparatus for stereotactic surgery on a body. The apparatus includes a guidance fixture and a controller that is coupled to the guidance fixture. The guidance fixture includes (a) a mounting base for attachment to the body, (b) a controllable instrument drive for moving a surgical instrument along a constrained trajectory in response to a drive control signal, (c) an actuated adjustment mechanism coupled between the mounting base and the controllable instrument drive for adjusting an orientation of the constrained trajectory relative to the mounting base in response to an adjustment control signal, and (d) a sensor system for providing signals encoding the orientation of the constrained trajectory and encoding a position of the surgical instrument along the constrained trajectory. The controller accepts signals provided by the sensor system, accepts a control input, computes drive control and adjustment control signals in response to the signals provided by the sensor system and the control input, and provides the drive control signal and the adjustment control signal to the guidance fixture.
The apparatus can include one or more of the following features.
A display for accepting a display signal from the controller. The controller determines the display signal in response to the signals provided by the sensor system and an image of the body such that the location and orientation of the surgical instrument is displayed in conjunction with the image of the body.
A processor programmed to execute a procedure in response to a control input, such that execution of the procedure determines the drive control and the adjustment control signals.
A communication channel, such as a data communication channel or a wireless communication link, coupling the controller and the guidance fixture for passing the drive control and adjustment control signals.
In another aspect, in general, the invention is a guidance fixture for stereotactic surgery on a body. The guidance fixture includes an instrument guide for moving a surgical instrument along a constrained trajectory relative to the instrument guide as well as an adjustable base for supporting the instrument guide. The adjustable base includes (a) a mounting base for attachment to the body having a central axis, and (b) an adjustment mechanism coupled between the mounting base and the instrument guide. A configuration of the adjustment mechanism determines an orientation of the instrument guide relative to the central axis of the mounting base. The guidance fixture also includes a signaling device coupled to the adjustment mechanism for providing a configuration signal, such as an electrical, mechanical, or optical signal, encoding the configuration of the adjustment mechanism.
The signaling device can include a number of encoders coupled to the adjustment mechanism for generating the configuration signal. For example, a first encoder generates a rotation signal encoding an angle of rotation of the constrained trajectory around the central axis of the mounting base, and a second encoder generates a pivoting signal encoding an angle between the constrained trajectory and the central axis of the mounting base.
The instrument guide can include a drive mechanism for positioning the surgical instrument along the constrained trajectory, and the signaling device can further include an encoder, such as an electrical linear encoder, coupled to the drive mechanism for generating a position signal encoding a position of the surgical instrument along the constrained trajectory.
The guidance fixture can further include an actuation device, including, for example a number of electrical motors or hydraulic actuators, coupled to the adjustment mechanism for adjusting the configuration of the adjustment mechanism.
An advantage of the invention is that once the guidance fixture is attached to the body and located in reference to the three-dimensional image of the body, the orientation and position of the guidance fixture can be tracked using the sensor system. This can provide more accurate tracking of the position and orientation of the guidance fixture then by continually tracking the guidance fixture using a remote sensing device, such as a camera, and does not require tracking sensors to be continuously visible to the remote sensing device. A patient can be free to move around and, in the case of a wireless communication link passing the sensor signals, the patient can be completely untethered. By also generating a sensor signal that encodes the location of an instrument relative to the guidance fixture, the three-dimensional location of the instrument can be continuously determined based on sensor signals, and displayed in conjunction with a scanned image of the body, thereby providing accurate real-time feedback to a surgeon.
Another advantage is that when the guidance fixture is also actuated, then adjustment of the fixture and positioning of an instrument relative to the fixture can be controlled remotely. Remote control allows use control systems, such as feedback control systems, coupled between an operator and the fixture. Also, automated procedures, for example controlled by a computer program, can perform complex or tedious procedures, for example, mapping an area of the brain by repeated electrical measurements at points on a grid. Remote control also permits tele-robotic operation in which a surgeon does not have to be present at the same location as the patient. Once the fixture is attached and registered to the patient, only the sensor and control signals are needed to pass between the guidance fixture and the surgeon. Force feedback signals from the fixture can further improve the ability of the surgeon to accurately control the position of the instrument.
Other features and advantages are apparent from the following description and from the claims.